Wireless cellular communication networks incorporate a number of mobile user devices and a number of NodeBs. A NodeB is generally a fixed station, and may also be called a base transceiver system (BTS), an access point (AP), a base station (BS), or some other equivalent terminology. As improvements of networks are made, the NodeB functionality evolves, so a NodeB is sometimes also referred to as an evolved NodeB (eNB). In general, NodeB hardware, when deployed, is fixed and stationary, while the user equipment hardware is portable.
In contrast to NodeB, the mobile user equipment can comprise portable hardware. User equipment (UE), also commonly referred to as a terminal or a mobile station, may be fixed or mobile device, and may be a wireless device, a cellular phone, a personal digital assistant (PDA), a wireless modem card, and so on. Uplink communication (UL) refers to a communication from the mobile UE to the NodeB, whereas downlink (DL) refers to communication from the NodeB to the mobile UE. Each NodeB contains radio frequency transmitter(s) and the receiver(s) used to communicate directly with the mobiles, which move freely around it. Similarly, each mobile UE contains radio frequency transmitter(s) and the receiver(s) used to communicate directly with the NodeB. In cellular networks, the mobiles cannot communicate directly with each other but have to communicate with the NodeB.
Wireless users require high-speed connections that support real time video, streaming music, and other multimedia applications. As a result, demands on wireless networks approach the broadband speeds and user experience provided by traditional DSL and cable modem wireline service. Wireless networks continue to evolve to next-generation packet architectures capable of supporting enhanced broadband connections with the introduction of 4G systems.
The higher speeds and capacity provided by 4G wireless networks put strain on backhaul networks and the carriers providing backhaul services as the transport requirements increase. Providers are shifting from traditional TDM transport in 2G and 3G networks to packet transport to support higher data rates, reduce network latency, and support flexible channel bandwidths in 4G networks. The backhaul networks require efficient Bit-Error-Rate (BER) performance to support 4G mobile networks.
Error-control coding techniques may detect and possibly correct errors that occur when messages are transmitted in a communication channel. To accomplish this, the encoder transmits not only the information symbols but also extra redundant parity symbols. The decoder interprets what it receives, using the redundant symbols to detect and possibly correct whatever errors occurred during transmission.
Block coding is a special case of error-control coding. Block-coding techniques map a fixed number of message symbols to a fixed number of code symbols. A block coder treats each block of data independently and is a memory-less device. The information to be encoded consists of message symbols and the code that is produced consists of codewords. Each block of K message symbols is encoded into a codeword that consists of N message symbols. K is called the message length, N is called the codeword length, and the code is called an [N,K] code.
Turbo codes are a class of high-performance error correction codes developed in 1993 which are finding use in deep space satellite communications and other applications where designers seek to achieve maximal information transfer over a limited-bandwidth communication link in the presence of data-corrupting noise. The channel coding scheme for transport blocks in LTE is Turbo Coding with a coding rate of R=1/3, using two 8-state constituent encoders and a contention-free quadratic permutation polynomial (QPP) turbo code internal interleaver. Trellis termination is used for the turbo coding. Before the turbo coding, transport blocks are segmented into byte aligned segments with a maximum information block size of 6144 bits. Error detection is supported by the use of 24 bit CRC. The 1/3 coding rate triples the bit-count for transmission of the block. In LTE, a circular buffer rate matching (CBRM) technique is used in which the systematic bits and the parity bits are placed in a circular buffer. During readout for a selected code rate, if the end of the buffer is reached reading continues by wrapping around to the beginning of the buffer The general operations of channel coding are described in the EUTRA specifications, for example: “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (TS36.212, Release 12.4),” which is incorporated by reference herein.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.